1. Field of the Invention
The present invention relates to a data encryption method, and more particularly, to a data encryption method implemented on a pattern displaying medium with at least two types of ink.
2. Description of the Prior Art
From ancient times, many languages have been represented with pictures or patterns for indicating respective meanings, such as Pictograph or other ancient languages. Therefore, various meaningful patterns, or even permutations and combinations of pictures and patterns, serve as foundations of transmitting messages. Under certain circumstances, a highly classified message has to be transmitted from a person A to another person B, and cannot be retrieved and realized by still another person C, who is other than both the people A and B. Such a condition may be fulfilled by using a technique called steganography for hiding information. Steganography is a technique of hiding meaningful messages within pictures, languages, or objects, is an ancient technique utilized for thousands of years, and is an effective technique of transmitting messages without letting the transmitted messages perceived by someone else, who needs not to know the transmitted messages. Besides purposes related to communication systems, steganography may also applied on characters and pictures, both of which are shown on surfaces of products and are utilized for hiding information from being perceived by consumers, so as to rapidly confirm product-related messages, which consumers need not to know.
For example, within bar codes utilized on a wide variety of products, no information is exposed to consumers. In other words, the bar codes do not bring any meaningful information for the consumers. However, for a product management who has a scanner for decrypting the bar codes, information hidden within the bar codes is meaningful so that a scanned product may be directly recognized. Braille may also be utilized on a toy, different parts of which are padded with encrypted patterns or characters. When the encrypted patterns or characters are scanned or triggered by specific commands, corresponding messages are decrypted or issued. However, the decrypted or issued messages are conventionally hidden in a visible manner for the naked eye. Moreover, a degree of hiding information is often restricted by patterns or colors adhered to the surface of the object. Therefore, an amount of hidden messages on the surface of the object is also strictly restricted.
Please refer to FIG. 1 and FIG. 2, which are diagrams of a disclosed method for indicating data by pointers indicated by patterns according to US Publication Patent No. 2003/0133164. As shown in FIG. 1, data are indicated with a plurality of data blocks 120 on a pattern displaying medium 110 in the disclosed method. Each data block 120 is utilized for indicating a different datum, and is located at a different coordinate on the pattern displaying medium 110. Note that marking a plurality of coordinates on the pattern displaying medium 110 includes setting an origin on the pattern displaying medium 110, and inducting positions relative to the set origin one by one with the aid of interpolation so that the territory of each data block 120 is not overlapped to generating errors in indicating data. As shown in FIG. 2, a data block 120 covers a header region 122 and a data region 124, which includes a plurality of data units 126. Each data unit 126 indicates different bits with two states. In other words, each data unit 126 is utilized for indicating a single binary bit. Therefore, when there are n-by-n data units 126 in a data region 124, the data region 124 is utilized for indicating a data string having n-by-n bits, where n is a positive integer. Data indicated in a header region 122 of each data block 120 is the same.
While data indicated on the pattern displaying medium 110 are to be read, a preset scanning device is utilized for scanning characteristics of any data block 120 on the pattern displaying medium 110. A header region 122 of a data block 120 is the first to be scanned so as to recognize a domain covered by the data block 120. Then a data region 124 of the data block 120 is scanned for recognizing an indicated bit of each data unit 126 within the scanned data region 124. Data on the pattern displaying medium 110 are marked with ink capable of reflecting visible lights, and are public to any observer of the pattern displaying medium 110. For the purpose of information hiding, existences or meaningful information of the data blocks 120 must be concealed from those who need not to know hidden meanings of indicated data on the data blocks 120 of the pattern displaying medium 110, and therefore, ink utilized on the header region 122 and the data region 124 of each data block 120 is capable of absorbing infrared, and is of a same type. Besides, decreasing an amount of marked data units 126 of each data region 124 may also be regarded as a preferable technique in concealing the existences of data blocks 120 from being perceived by observers. Under the abovementioned circumstances, when the method disclosed in FIG. 1 and FIG. 2 is utilized on conventional products, observers may merely perceive obvious characteristics, such as trademarks on surfaces of the products, other than the plurality of marked data blocks 120 so that information hiding is fulfilled.
However, there are two obvious defects in the method disclosed in FIG. 1 and FIG. 2. First, for preventing domains of the plurality of data blocks from being overlapped with each other, interpolation has to be utilized for locating each data block 120 with the aid of the predetermined origin. However, when marked coordinates on the pattern displaying medium 110 are not located at precise positions, the plurality of data blocks 120 are likely to be located at erroneous positions, where positioning errors of the marked coordinates may be generated by unpredicted vibrations or jitters of the pattern displaying medium 110. Second, when there are positioning errors in the indicated data within the plurality of data blocks 120, positioning errors of the coordinates inducted by interpolation are also significantly generated as a result of the domino effect. No matter which one of the discussed situation happens, positioning errors are inevitably generated in most data blocks 120 on the pattern displaying medium 110 so that the information hidden in the data blocks 120 cannot be precisely and completely read. Moreover, since a same type of ink for absorbing infrared is utilized for marking both the header region 122 and the data region 124 of each data block 120, while any one group among the marked coordinates and the data blocks has positioning errors, the other group must be brought with positioning errors as well. Therefore, the positioning errors are likely generated in the plurality of data blocks 120 on the pattern displaying medium 110, and even a yield of each product utilizing the pattern displaying medium 110 is significantly reduced.